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What is Unique constraints ?

Unique constraints are like alternative primary key constraints. A unique constraint defines a column, or series of columns, that must be unique in value. You can have a number of unique constraints defined and the columns can have NULL values in them, unlike a column that belongs to a primary key constraint.   If you need to add unique key constraints to a table after the fact, simply use the alter table command.




CREATE TABLE table_name


 column1 datatype Unique,

 column1 datatype,

 column1 datatype


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